: The long-term objective of this project is to fully characterize the ends of human chromosomes. One outcome of these investigations will be construction of fully integrated regional genetic and physical maps with ultimate resolution in the DNA sequence. The goals for the next three years are to generally improve the telomere maps by developing primary resources (clones, genetic markers, STSs) and constructing baseline integrated maps. Selected telomere regions will be intensively mapped and the investigators will test the feasibility of sequencing genomic DNA from several regions adjacent to the terminal T2AU3 repeats. In addition, they propose to maintain a comprehensive electronic telomere resource, TeIDB, that will facilitate communication and sharing of telomere data within the scientific community. The specific aims to be achieved during the next three years are to: 1) Continue genetic mapping of selected human telomere regions and develop highly informative microsatellite markers for telomere regions for which such markers have not yet been reported. The new microsatellite markers will be incorporated into multipoint and 2D crossover meiotic telomere region maps. 2) Characterize the genomic structure or selected human telomere regions. 3) Utilize all available physical and genetic mapping data to produce unified regional physical and genetic telomere maps. 4) Identify candidate clones for telomeres for which clones have not yet been identified. 5) Maintain the telomere database resource, TeIDB, which is currently available over the intemet (http://www.genlink.wustl.edu/teldb/).